GRB 050815

D. Fox (PSU), L. Barbier (GSFC), S. Barthelmy (GSFC), D. Burrows
(PSU), J. Cummings (GSFC/NRC), N. Gehrels (GSFC), O. Godet
(U. Leceister), S.T. Holland (GSFC/USRA), S. Hunsberger (PSU),
J. Kennea (PSU), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
F. Marshall (GSFC), D. Morris (PSU), D. Palmer (LANL), K. Page
(U. Leicester), A. Parsons (GSFC), P. Roming (PSU), T. Sakamoto
(GSFC), P. Schady (PSU/UCL-MSSL), & E. Rol (Leceister) report on
behalf of the Swift team:

At 17:25:19 UT, Swift-BAT triggered and located GRB050815
(trigger=150532).  The BAT on-board calculated location is RA,Dec
293.575d,+9.166d {19h 34m 18s,+09d 09' 59"}, with an uncertainty of 2
arcmin (radius, 90% containment, stat+sys).  The BAT light curve shows
two peaks in 5 sec and possible low energy emission out to ~30 sec.
The peak count rate was ~1000 counts/sec (15-350 keV), at ~2 seconds
after the trigger.

The S/C slewed immediately and the XRT began taking data at 17:26:28,
70 s after the BAT trigger.  The XRT on-board centroid algorithm did
not converge and no prompt position is available.  However, the XRT
lightcurve shows evidence of a decaying source in the field of view.
We are waiting for down-linked data to determine a position.

The UVOT began observing the position of trigger #150532 at 17:26:25.5
UT, 67 s after the BAT trigger.  In a 100 s V-band image, no new
source is detected with respect to the DSS down to a 5 sigma upper
limit of 18.1 mag.  The estimated extinction in this direction is A_V
~ 1.6 magnitudes.  The UVOT image gives 55% coverage of the BAT error
circle.  The BAT source is located in a crowded star field.

D. C. Morris, D. N. Burrows, J. A. Kennea, J. L. Racusin (PSU), and N. 
Gehrels (GSFC) report on behalf of the Swift XRT team:

The Swift BAT instrument detected GRB 050815 at 17:25:19 UT (Fox et al. 
2005, GCN 3811
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 ).  The observatory executed an automated slew to the BAT 
position and the XRT began taking data at 17:26:28 UT (69 seconds after 
the BAT trigger). Due to a low source count rate, the XRT did not succeed 
in calculating an on-board centroid.  In the ground-processed data, we 
find a faint, uncataloged, fading X-ray source located at:

RA(J2000) = 19:34:22.9
Dec(J2000) = +09:08:46.1

We identify this as the afterglow of the GRB.  We estimate an uncertainty 
of about 8 arcseconds radius (90% containment).  This source is located 
102 arcseconds from the BAT position in GCN 3811
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 .

Fang Yuan, E.S. Rykoff (U Mich) report on behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, 
responded to GRB 050815 (Swift trigger 150532), producing images 
beginning 7.2 s after the GCN notice time. An automated response took 
the first image at 17:25:54.2 UT, 35.5 s after the burst, under fair 
conditions. We took 10 5-sec, 10 20-sec and 130 60-sec eposures. These 
unfiltered images are calibrated relative to USNO A2.0 (R).

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma error circle, for both single images and coadding into sets of 
10; however, we are limited as the field is severely crowded. 
Furthermore, we do not detect any new objects in the XRT error circle 
(Morris et al, GCN 3812
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 ). Individual images have limiting magnitudes 
ranging from 14.9-15.8; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
17:25:54.2   17:25:59.2         5     14.9           35.5       N
17:25:54.2   17:27:25.2        91     15.8           35.5       Y
17:27:25.9   17:32:20.9       295     16.1          127.2       Y

D. Hullinger (GSFC/UMD), M. Ajello (MPE), L. Barbier (GSFC),
S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL),
R. Fink (GSFC), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC)
on behalf of the Swift-BAT team:

Using the full data set from the recent telemetry downlink, we report
further analysis of Swift-BAT GRB 050815 (trigger #150532)
(Fox, et al., GCN 3811
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 ).  The ground-analysis position is
RA,Dec 293.579,+9.145 (J2000) with an uncertainty of 2 arcmin
(radius, 90%, stat+sys).  This is 59 arcsec from the XRT
refined position (Morris et al., GCN 3812
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 ).  The light curve
shows an increase in emission starting at T-2 sec with a peak
at ~T+1 sec and the burst is over by T+4 sec.  T90 is 2.8 +/-1 sec.
Fitting a simple power law over the interval from T-0.7 to T+2.4 sec,
the photon index is 1.8 +/- 0.2 with a fluence of
1.5 +/- 0.4 x 10^-7 erg/cm^2 in the 15-350 keV band (90% c.l.).
The peak flux in a 1-sec wide window starting at T-0.1 seconds
is 0.66 +/- 0.14 ph/cm^2/sec (15-350 keV).  Based on the duration
of >2 sec and the soft spectrum, it does not appear that this burst
is in the short-hard category.

D. C. Morris, D. N. Burrows, J. A. Kennea, J. L. Racusin (PSU), and N. 
Gehrels (GSFC) report on behalf of the Swift XRT team:

We have analysed the first three orbits of data for GRB050815 (GCN 3811
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 , 
Fox et al., 2005).  Using xrtcentoid, the refined position is:

RA(J2000) = 19h 34m 23.2s
Dec(J2000) = +09d 08' 49.6"

with an uncertainty of 8 arcsec. This is 5.6 arcsec from the original 
XRT position (GCN 3812
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 , Morris et al., 2005).

The XRT began taking data at 17:26:28UT, 69 seconds after the BAT 
trigger. The XRT collected data for only 123s during the first orbit 
before the source was occulted. The data show a faint source in the 
first orbit and suggest an initially shallow decay index of ~-0.2 
followed by a break occuring somewhere between 192s and 3000s to a 
steeper decay index of ~-2.1.

The spectrum is well fit (reduced chi-sq of 1.03 for 9 dof) by a power 
law with neutral hydrogen consistent with the galactic column density of 
2.7e21:

gamma=1.4 + / - 0.2
NH=2.1e21 + / - 7e20

Fixing the NH to the galactic column density also returns a good fit 
(reduced chi-sq of 1.00 for 10 dof):

gamma=1.5 + / - 0.1

The count rate at 10000s after the trigger is ~0.015 cts/s which 
converts to an unabsorbed flux of 9e-13 ergs cm^-2 s^-1 from 0.2-10keV.

P. Schady (MSSL/PSU), D. Fox (PSU), P. Roming (PSU), A. Cucchiara (PSU), 
M. Still (GSFC), S.T. Holland (GSFC/USRA) K. Mason (MSSL), A. Blustin 
(MSSL), N. Gehrels (GSFC), on behalf of the Swift UVOT team

The Swift Ultra-Violet Telescope (UVOT) began observations of GRB050815 on 
August 15th, 2005 at 17:26:25.6 UT, 67s after the BAT trigger. The UVOT 
took a 100s exposure in the V band and two 10s exposures in the M1 and W2 
UV filters before the source was occulted by the Earth. The next set of 
observations were made ~1hr after the BAT trigger.

Anylsis of the early time data reveals an uncatalogued source in the V 
band at position

Ra, Dec = 19:34:23.147, +09:08:47.47

with an estimated uncertainty of 0.5". Astrometry was performed using 
stars from the USNO-catalogue. The source is no longer detected in the 
second epoch of V band images, confirming it's fading nature, and leading 
us to conclude this to be the afterglow. No detections are made in any 
other of the UVOT filters at the 3-sigma significance level. 

Photometry carried out on this source requires additional care due to the 
proximity ofvarious bright stars (~16-18mag). We estimate the afterglow to 
have decayed by about 1 magnitude in 1 hour. Further analysis is still
undergoing.

P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of a
larger collaboration:

"We have undertaken VLA observations at a frequency of 8.46 GHz toward
GRB 050815 (GCN 3814
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 ) on August 17.05 UT. No radio afterglow is
detected. At the position of the optical afterglow (GCN 3817
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 ) the
point-source limit is 77 +/- 45 microJy.  No further observations are
planned.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."

D. Sharapov,  G. Abdullaeva, M. Ibrahimov (MAO), A.Pozanenko (IKI),
V.Rumyantsev (CrAO) on behalf of larger GRB follow up collaboration report:

We observed the XRT error box (Morris et al, GCNs 3812
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 ,3816
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 ) of GRB050815
(Fox et al, GCN  3811
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 )  with 1.5m telescope of Maidanak Astronomical
Observatory. Set of  R images were taken between (UT) 17:26 - 19:04, on
August 16.

We do not detect the OT  (Schady et al, GCN 3817
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 ) in a stacked image.
Limiting magnitude of the stacked image (14x300 s) is R ~ 22.5.  Detailed
photometry of the observation is underway.

The stacked image can be found in
http://grb.rssi.ru/GRB050815/grb050815_050816_AZT22_R.jpg.

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